1. Field of the Invention
The present invention relates generally to telecommunications, and particularly to a method and device for evaluating the quality of signals transmitted in a network.
2. Technical Background
Telephone connections have always been subject to impairments in the form of noise, attenuation, distortion, cross-talk and echo. Such impairments are particularly common to analog portions of the network, such as subscriber loops and frequency domain multiplexing equipment. Digital transmission alleviates many of these problems but also introduces quantization noise and other waveform distortions resulting from data transmission errors. Thus, a typical telephone connection completed over a long distance network is exposed to impairments, regardless of the transmission technology or combination of transmission technologies employed.
Such impairments can produce conditions that a telephone customer will find objectionable or intolerable. It is particularly frustrating when the malfunctioning piece of equipment is an automated system, such as a menu-driven voice response unit. When there is a high incidence of problems with a given unit, customers may simply become irritated and hang-up. This translates into a loss of business for the vendor employing the malfunctioning equipment. If the problem is associated with the quality of the network, the vendor may be tempted to change carriers. Thus, the quality of telephone connections is a major factor affecting the reputation and marketability of long distance telephone services.
In order to measure transmission quality over a telecommunications link, it is frequently necessary or useful to compare a received signal to a known reference waveform. To perform this comparison, the received signal must be synchronized with the reference signal. The received signal is then compared with a perfect version of the signal to obtain a point-by-point determination of how the received amplitude signal differs from the perfect version of the signal. In another scenario requiring such synchronization, it is desirable to be able to determine if a certain bong-tone or pure-tone was transmitted. In yet another scenario, a vendor""s equipment may be programmed to transmit a particular voice announcement, or in a menu-driven system, a series of tones and/or voice announcements. The received signal must be processed to automatically determine whether the vendor""s equipment is functioning properly. What is needed is a method and device for detecting a waveform, and comparing the detected waveform to a reference waveform with proper synchronization.
In one approach that has been taken, a frequency domain analysis employing Fast-Fourier-Transforms (FFT) is used to compare a received signal to a known reference waveform. This approach necessitates the use of a digital signal processor (DSP). While DSP systems certainly are effective, DSP integrated circuits (IC) are expensive. It would be very difficult to upgrade an existing microprocessor based Telephone Quality Measurement System (TQMS).
What is needed is a compact, inexpensive, and fast method for synchronizing and comparing a received signal to a known reference waveform. What is also needed is a way to upgrade existing measurement systems without adding unnecessary components and expense. Preferably, the upgrade can be accomplished by merely changing or adding software.
The present invention provides a compact, inexpensive, and fast method for synchronizing and comparing a received signal to a known reference waveform. The present invention can also be used to upgrade existing test and measurement systems without adding unnecessary components and expense. In some circumstances, the present invention can be used to upgrade an existing system by adding software.
One aspect of the present invention is a device for detecting a predetermined waveform in a signal. The device includes a memory element for storing at least one reference set of encoded values, the at least one reference set representing an encoded version of the predetermined waveform. An encoder is adapted to encode the signal to thereby obtain at least one signal set of encoded values. A processor is coupled to the memory element and the encoder. The processor is operative to calculate at least one statistical correlation coefficient of the reference set and the at least one signal set, whereby the predetermined waveform is detected in the signal if the at least one statistical correlation coefficient is greater than or equal to a predetermined threshold value.
In another aspect, the present invention includes a method for detecting a predetermined waveform in a signal. The method includes providing at least one reference set of encoded values, the at least one reference set representing an encoded version of the predetermined waveform. The signal is encoded to thereby obtain at least one signal set of encoded values. At least one statistical correlation coefficient of the at least one reference set and the at least one signal set is calculated, whereby the predetermined waveform is detected in the signal if the at least one statistical correlation coefficient is greater than a predetermined threshold value.
In another aspect, the present invention includes a device for detecting a predetermined waveform in a signal transmitted by a telecommunications system in a network. The device includes an interface unit coupled to the network. The interface unit is operative to automatically establish a telephonic connection between the device and the telecommunications system and capture the signal transmitted by the telecommunications system. An encoder is coupled to the interface unit. The encoder is operative to encode the signal to thereby obtain at least one signal set of encoded values. A processor is coupled to the encoder, the processor being operative to calculate at least one statistical correlation coefficient of at least one reference set and the at least one signal set, whereby the predetermined waveform is detected in the signal if the at least one statistical correlation coefficient is greater than a predetermined threshold value.
In another aspect, the present invention includes a computer readable medium having computer executable instructions for performing a method. The method includes obtaining a reference set of encoded values, the reference set representing an encoded version of a predetermined waveform. A signal is encoded to thereby obtain at least one signal set of encoded values. At least one statistical correlation coefficient of the reference set and the at least one signal set is calculated. The at least one statistical correlation coefficient is compared with a predetermined threshold value, whereby it is determined that the signal includes the predetermined waveform if the at least one statistical correlation coefficient is greater than a predetermined threshold value.
In another aspect, the present invention includes a device for determining whether a signal is a pure tone. The device includes an encoder operative to encode a portion of the signal to thereby obtain a reference set of PCM encoded values. A processor is coupled to the encoder. The processor is programmed to: calculate a second-differences of the signal to thereby obtain a second-differences set of encoded values; calculate a statistical correlation coefficient of the reference set and the second-differences set; and compare the statistical correlation coefficient to a predetermined threshold, whereby the signal is determined to be a pure tone if the statistical correlation coefficient is greater than the predetermined threshold value.
In another aspect, the present invention includes a method for determining whether a signal is a pure tone. The method includes encoding at least a portion of the signal to thereby obtain a reference set of encoded values. The second-differences of the signal is calculated to thereby obtain a second-differences set of encoded values. A statistical correlation coefficient of the reference set and the second-differences set is calculated. The statistical correlation coefficient is compared with a predetermined threshold, whereby the signal is determined to be a pure tone if the statistical correlation coefficient is greater than the predetermined threshold value.
In another aspect, the present invention includes a device for detecting a predetermined waveform in a signal. The device includes a memory element for storing at least one reference set of encoded values, the at least one reference set representing an encoded version of the predetermined waveform. An encoder is adapted to encode the signal to thereby obtain at least one signal set of encoded values. A processor is programmed to encode at least a portion of the signal to thereby obtain a reference set of encoded values, calculate the second-differences of the signal to thereby obtain a second-differences set of encoded values, calculate a statistical correlation coefficient of the reference set and the second-differences set, and compare the statistical correlation coefficient to a predetermined threshold. The signal is determined to be a pure tone if the statistical correlation coefficient is greater than the predetermined threshold value.
In another aspect, the present invention includes a method for synchronizing a received signal with a predetermined waveform. The method includes providing a reference set of encoded values, the reference set representing an encoded version of the predetermined waveform. The signal is encoded to thereby obtain a plurality of encoded values. A plurality of correlation coefficients is calculated for the reference set and each of a plurality of signal sets. A maximum value correlation coefficient of the plurality of correlation coefficients is determined. The reference set is aligned with a signal set corresponding to the maximum value correlation coefficient.
In another aspect, the present invention includes a device for detecting a predetermined waveform in a signal. The device includes a memory element for storing at least one reference set of encoded values, the at least one reference set representing an encoded version of the predetermined waveform. An encoder is adapted to encode the signal to thereby obtain at least one signal set of encoded values. A processor is programmed to provide a reference set of encoded values, the reference set representing an encoded version of the predetermined waveform. The processor is also programmed to encode the signal to thereby obtain a plurality of encoded values, calculate a plurality of correlation coefficients for the reference set and each of a plurality of signal sets, determine a maximum value correlation coefficient of the plurality of correlation coefficients, and align the reference set with a signal set corresponding to the maximum value correlation coefficient.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.